We recently purchased a 2005 xB used from a dealer..that has 18 inch wheels and has been lowered about 2 inches
it looks great

here is my question..I am running 18 inch rims with 215/35R18 tires
will running a wheel this size change the speedometer readings and mileage?

any ideas would be greatly appreciated...thanks in advance

 

Try here to see what you think
just start with the stock sizes and put in what your current setup is.

http://www.miata.net/garage/tirecalc.html

 

that is awesome thanks

 

Here is another nice calculator link. http://www.rims-n-tires.com/rt_specs.jsp?postId=906

 

thanks I really appreciate the links..besides styling..one of the biggest motivators for us in deciding to purchase our xB was the gas mileage
the reason I was asking about speedo error..is that it seems
we are only getting about 22 miles to the gallon..and it just doesnt seem correct

also..I have no idea what size tires came on this thing stock

any ideas?

 

Stock size is 185/60/15 on 15X6" wheels with 38mm offset. Lug pattern is 4X100mm. Hope this helps!

 

yes that helps...I notice you are running the same size tires that I have..

your xB is pretty sweet BTW!!!

just curious..did you have your speedo recalibrated? and did you notice anything like dropped gas mileage or speedometer error?

I'm going to use a portable GPS and see if there is any speedo error...
I'll let you know what I find out if your interested?

 

Thanks! Didn't need to re-calibrate the speedo cause it's almost dead on. The mpgs do drop some because the 18's weigh a bit more plus the added drag from the wider tire footprint.
Def. let me know how the gps thing goes on actual speed. I'm very curious.
When I need new tires I'll prolly move up to 215/40/18 just to have a bit more sidewall height.

 

I'll have the GPS info for you by tomorrow..

in the mean time what I found out on paper is..at 60 MPH
I'm really supposed to be going 60.5 MPH
with my 18's

I'll check that out and let you know

 

the speedo on my rs 4.0 is off by 2mph slower that what it is reading
so if speedo is saying 45 i'm reely doing 42
hope this helps

 

Mileage can deteriorate badly in winter, with warmup time and sitting around in traffic taking their toll...

Lots of short hops doesn't help, either, with cold temps preventing the engine from warming up, getting onto the closed loop feedback from the O2 sensor that really improves mileage...

If you're like me, having a lead foot doesn't help, either...

Several posters have noted that owning and using a scangauge really helps them to drive for better mileage- it can give continuous mpg readings...

 

I gotta get me one of those scanguages. I'm finding that the winter blend 87 octane is absolute poo poo. I'm having to run mid-grade 89-90 during the winter time just to avoid spark knock in most our vehicles that normally run fine on 87.

 

I just got back from the 60 MPH, GPS vs speedo comparison
and I found that at 60 MPH as indicated on the speedo...the GPS says we were going 59

I'm not sure how thats going to equate into MPG
But I certainly appreciate the feedback and suggestions

my test with the GPS was in no way a scientific test by any means
but I think my results are pretty accurate

 

If you have mile markers along the highway you can tell if your odometer is correct. Zero the trip odo at a mile marker and drive 10 miles or so. See if you are pretty close to accurate. Of course the markers could be off slightly. I have fould that over a distance of several miles mine is pretty close, ie. I am right at the marker as the trip odo changes. Also drive a constant 60mph, if possible, to compare speedo and odo.

Most speedometers are within 1-2 mph with stock wkeels but I have seen the odo off as much as .1 miles while the wpeedo was correct. The one I am thinking about indicated .9 miles for every actual mile driven. After driving 200 miles it indicated 180. That made for some bad mpg numbers.

 

thanks flyerI

I'll give it a try..my GPS'r also logs distance...I should check all 3 figures..
thx for the suggestion